Recently, as a high energy-density battery, nonaqueous electrolyte batteries such as lithium ion secondary batteries have been developed. Nonaqueous electrolyte batteries are anticipated, for example, as a power source for vehicles such as hybrid automobiles and electric cars, and as a power source for large storage use. In particular, regarding use in vehicles, there is demand for the nonaqueous electrolyte battery to have other good performances such as rapid charge-and-discharge performances and long-term reliability, as well. Being capable of rapid charge-and-discharge, nonaqueous electrolyte batteries have the benefit that charging time is remarkably short, and are able to improve motive performances, for example, in hybrid automobiles. Furthermore, the battery can also efficiently recover regenerative energy from motive force of the vehicle.
Rapid charge-and-discharge becomes possible by rapid migration of electrons and lithium ions between the positive electrode and the negative electrode. However, when a battery using a carbon-based negative electrode including a carbonaceous material is repeatedly subjected to rapid charge-and-discharge, dendrite of metallic lithium may sometimes precipitate on the electrode. Dendrites cause internal short circuits, and as a result raise concern of heat generation and ignition.
In the light of this, batteries using a metal composite oxide as a negative electrode active material in place of a carbonaceous material have been developed. In particular, in a battery using titanium oxide as the negative electrode active material, rapid charge-and-discharge can be stably performed. Such a battery also has a longer life than those using a negative electrode with carbonaceous material.
However, compared to carbonaceous materials, oxides of titanium have a higher potential (is more noble) relative to metallic lithium. Furthermore, oxides of titanium have a lower capacity per mass. Therefore, a battery using an oxide of titanium as the negative electrode active material has a problem that the energy density is lower. In addition, there is room for improvement in output and cycle life of the battery.